Hemodynamic and renal functional studies will be conducted in isolated blood perfused canine kidneys and in dogs in vivo. The effects of prostaglandins and proetolysis on tachyphylaxis to angiotensin will be assessed. Specific tissue enzymes and their inhibitors will be infused into isolated kidneys to determine if these reverse tachyphylaxis. Similar studies will be conducted in dogs in vivo and the relationship of these maneuvers to renal failure will be determined. Secretory mechanisms for catecholamines will be evaluated in the isolated kidney.